✅ e2e mock: add AppSec scenario + custom remediation header assertion

Address review feedback on the binary e2e suite:

- mocklapi: add an AppSec WAF stand-in (--appsec-addr) that blocks any URI
  containing "rpc2" — the exact probe from examples/appsec-enabled — and allows
  the rest. Lets the suite exercise the plugin's AppSec wiring (header
  forwarding + allow/block enforcement) without the real CRS engine.
- new scenarios/appsec: benign request passes, /foo/rpc2 is 403.
- custom-ban-page: assert the banned response carries the custom remediation
  header (remediationHeadersCustomName), per review.
- README: drop the "don't open issues / AppSec intentionally absent" framing;
  describe what the suite actually covers, including AppSec wiring.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/e2e/mock/scenarios/appsec/dynamic.yml

@@ -0,0 +1,29 @@
+http:
+  routers:
+    r:
+      rule: "PathPrefix(`/foo`)"
+      entryPoints:
+        - web
+      service: backend
+      middlewares:
+        - bouncer
+  services:
+    backend:
+      loadBalancer:
+        servers:
+          - url: "@@BACKEND_URL@@"
+  middlewares:
+    bouncer:
+      plugin:
+        bouncer:
+          enabled: "true"
+          # IP bouncing disabled — this scenario exercises AppSec only.
+          crowdsecMode: none
+          crowdsecLapiScheme: http
+          crowdsecLapiHost: "@@LAPI_HOST@@"
+          crowdsecLapiKey: "@@APIKEY@@"
+          crowdsecAppsecEnabled: "true"
+          crowdsecAppsecScheme: http
+          crowdsecAppsecHost: "@@APPSEC_HOST@@"
+          forwardedHeadersTrustedIps:
+            - "127.0.0.1/32"